Assessing the Radiative Cooling Effect of a New Urban Roof Material

Abstract:

Urban areas are home to more than half of the world’s population and are particularly vulnerable to many climate-driven risks, including intensified heat waves. To mitigate the urban heat stress, many innovative strategies have been developed and proposed such as albedo management (reflective material on rooftop and/or pavement to reduce solar energy absorption), green strategy (plant vegetation on rooftop and street trees to enhance evaporative cooling) and sustainable energy infrastructure (conversion of direct heating to energy resource such as solar photovoltaics). However, previous studies have largely reported a nighttime failure that these strategies often generate little cooling effects during nights. Here we utilize the Community Earth System Model (CESM) to evaluate, under realistic climate conditions, the potential cooling efficacy of a newly proposed roof coating material (Zhai et al., 2017) that seems promising to solve the nighttime urban heat problem via passive radiative cooling. Specifically, we parameterize the new roof material into CESM and conduct global simulations for 30 years under present-day climate, as well as for the 21^st century under future climate change scenarios under RCP (Representative Concentration Pathways) - SSP (Shared Socio-economic Pathways) framework. Preliminary results show that the new material effectively reduces urban surface air temperature and wet-bulb temperature during daytime, while the nighttime cooling effect depends on the meteorology, especially cloud cover. Our simulation also further reviews the underlying physical mechanism linked to such temperature reduction. The results help identify the prospects and limitations of passive radiative cooling strategy in mitigating urban heat stress and inform sustainable urban development.

Reference

Zhai, Y., Ma, Y., David, S. N., Zhao, D., Lou, R., Tan, G., . . . Yin, X. (2017). Scalable-manufactured randomized glass-polymer hybrid metamaterial for daytime radiative cooling. Science, 355(6329), 1062-1066.